By Mary Kenny

It's years since I'd been on a diet. In fact, I'd given up dieting, rather scornfully boasting that life is too short not to enjoy whatever food takes your fancy - and look at Catherine Deneuve anyway.

Reassuringly plumped: Catherine Deneuve still looks fabulous in her 70s

It's years since I'd been on a diet. In fact, I'd given up dieting, rather scornfully boasting that life is too short not to enjoy whatever food takes your fancy - and look at Catherine Deneuve anyway.

Catherine Deneuve, I went around saying, is the template and the examplar par excellence for old gals. Still great-looking, past 70, but visibly, filled out. A little stout around the waist and the hips, notice. And all the better for it.

Who needs to be a size 10 - or even 12 - in the senior years? What fool said: "You can never be too thin or too rich?" Some trophy wife who looks like an X-ray.

Denial, denial. Filled out is one thing, but when you're puffing while walking uphill, or you're being warned about diabetes, strokes, asthma and heart failure - such weight-related maladies now rising alarmingly among women - there's a different reason to address the weight issue.

It's not about getting into a size 10 frock any more. It's about health.

Being overweight - let's be honest and use the f-word: fat - can be truly bad for your health. You're carrying nearly 30 extra pounds of luggage, when you're two stone overweight, as I've been for the last few years, spouting denial-speak about Catherine Deneuve.

So, when January this year dawned, I took myself off to one of those weight-loss clubs which, for a modest sum of money, weigh you each week, and give you a book of guidance and a regular pep-talk about how to eat sensibly and lose weight.

The psychology of these organisations is based on three factors: (1) shame, (2) stigma and (3) paying a fee. By being weighed in a public place, you are ever so slightly ashamed of yourself, even though you are standing in a line of ladies - mostly - all of whom are an outsize model.

Nobody calls out the terrible secret of your weight, but you can see it yourself on the scales, and if, by the following week, you haven't lost any of that avoirdupois, you will feel, internally, the stigma.

'Slimming World' (as the particular organisation is called) goes to some length to assure us they won't show disapproval, only support, but human psychology is such, that you internalise the ritual of the weigh-in, and you know you'll feel mortified with yourself if, by the following week, you haven't reduced somewhat. The other motivation is very clever: money.

Psychoanalysts have traditionally claimed that paying them a fee while you lie on their couch talking about your unhappy childhood - that the fee paid is part of the cure.

Thus with slimming clubs: it's not exorbitant - £4.95 here - but it's just enough to make you feel, "I've paid for this: I must get the value out of it".

As for the books and the printed material which tell you how to lose weight - essentially, it's basic common sense.

There's a list of foods you can eat freely, whenever and at any time: fish, lean meat, poultry, vegetables, fruit, and fat-free or low-fat cheese.

There's a list of foods you can eat in moderate measures: cereal, soups, nuts and seeds, canned and cooked fruits. And there's a list of 'sins' or as they term it, 'syns' - sweets, biscuits, various breads (especially bad are croissants and bagels), cakes, cheeses, alcohol - which you should only have in limited form.

But this, too, is good psychology: many a diet fails because the dieter feels so deprived of food pleasures and treats. I'm miserable without chocolate.

On such guidelines, most people will lose weight over time and the idea is to take it slowly. Over a stretch of about 16 weeks, I've lost about a stone. I haven't always kept strictly to the regime: sometimes I've adapted it to suit my own needs or convenience. I like big breakfasts and small evening meals and I like the old suggestion you should "breakfast like a king, lunch like a lord and dine like a pauper". Sometimes a Bovril and a yoghurt will do me fine for supper. This wouldn't suit everyone (and I'm sure wouldn't fit in with Madame Deneuve's glittering lifestyle), but I can hack it.

But the fact is that you will lose weight on any regime which reduces fats and sugars (or excessive carbohydrates), measures the amount of food you eat, and which includes reasonable exercise. And there are many ways of tackling this.

My cousin very successfully follows The Fast Diet, which recommends two 'fast' days a week, and five days of eating normally (within reason).

A recent Danish report (by Signe Sorensen Torekov in Copenhagen) also found that if you weight-watch for a year, the body adjusts and you tend to keep the weight down after that.

The real secret of the slimmers' clubs is that the weekly weigh-in, and the collective will is a key part of the motivation - and commitment.

"I could lose the weight by doing it alone and using my own bathroom scales," said a woman sitting next to me. "But I need the motivation of the group. I also need to fork out the money, strange as it seems."

For some of us, we also need a stronger reason than appearance alone. And health is a stronger reason.

Sure, it's nice that when I start sorting out the summer clothes, that I may be able to fit into a size 12. Yet there is a downside: I was developing a couple of double chins as a fatty, which are now disappearing, leaving the old neck looking a bit scrawny.